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The present invention relates generally to the field of seismic data acquistion and processing.
A novel method and system of extraction of accurate compressional wave and shear wave velocities from land and marine multicomponent seismic data with improved quality and new information concerning the earth""s subsurface geological imaging and lithologic properties are disclosed. Additionally, an improved multicomponent seismic exploration technique is disclosed in which multicomponent seismic data is acquired and processed with more accurate velocities to produce better image and to extract more useful lithology information from the acquired data.
In conventional seismic data processing, the Dix equation is used to replace a stack of layers with a single layer of the same form to derive moveout P-wave velocity and interval velocities. In the standard P-wave case, the layers are parameterized by zero-offset travel time and moveout velocity. P-S converted wave velocity analysis follows the same methodology, but use layers parameterized by zero offset time, P-wave velocity, and S-wave velocity instead. Because it is difficult to estimate two velocity parameters simultaneously, the P-wave velocities are picked in the standard migration velocity analysis from Pxe2x80x94P data. The velocity ratio of RMS S-wave velocity divided by RMS P-wave are estimated for each zero-offset converted wave time by performing a non-hyperbolic Vs/Vp ratio coherency scan on the P-S converted wave data.
Taner and Koehler (1969) showed that the travel times of Pxe2x80x94P and Sxe2x80x94S reflected waves in a horizontally-layered medium are accurately approximated using a truncated power series, standard Dix-style Pxe2x80x94P and Sxe2x80x94S wave velocity analysis methods are based on this theory with the moveout power series truncated at the hyperbolic term. The type of velocity estimation method is not as useful for multicomponent processing as it is for Pxe2x80x94P and Sxe2x80x94S processing. For P-S converted wave processing, the moveout is not exactly hyperbolic even for the case of a single homogeneous layer. P-S converted wave processing algorithms based on hyperbolic moveout are useful only when the source-to-receiver offset is small compared to the target depth of the reflector. The traditional first-order approximation for P-S converted wave velocity analysis cannot provide accurate velocity information. The velocity and travel time errors largely occur for the shallow reflectors. These shallow errors will propagate, causing errors for deeper layers in the velocity inversion. The RMS velocity errors may propagate to the interval velocity. It is very difficulty to detect the accuracy of the interval velocities obtained from the Dix equation using simple hyperbolic approach. Therefore, there is a long felt need for a new method for extraction of accurate P-wave and S-wave velocities from multicomponent seismic data.
In one embodiment of the present invention, a novel method and system of geophysical exploration utilizing joint velocity inversion to extract accurate P-wave and S-wave interval velocities from multicomponent seismic data is provided. The measured P-wave and S-wave velocities are useful for many other seismic data processing to produce enhanced seismic traces for the upgraded delineation of subsurface structures and for the extraction of lithologic information. The geophysical exploration method comprises multicomponent seismic data pre-processing and interpretation.
In a further embodiment, a multicomponent seismic survey is laid out to acquire compressional wave data, and compressional to shear wave and shear wave to compressional wave (P-S) data without regard for or knowledge of the geological character of the earth""s surface and sub-surface formations. Seismic energy is imparted into earth""s sub-surface and multicomponents of the seismic signals were detected and recorded at selected receiver locations.
A further embodiment of the present invention comprises a method to accurately measure the effective P-wave and S-wave velocities using joint inversion, which allows us to treat the earth""s subsurface as a system and find out the linear or non-linear system response from acquired seismic data. It has the advantage of allowing the extraction of P-wave and S-wave velocities from the acquired seismic data without knowledge of the subsurface geology by an iterating process. This iterating process builds a stable velocity model by joint velocity inversion.
In a further embodiment, the method further comprises a velocity field decomposition and reconstruction to derive the wanted velocities. The estimated initial velocities are decomposed into an invertible form for the derivation of the P-wave and S-wave interval velocities. This process is different from conventional velocity inversion by Dix equation. It requires the use of at least two components of acquired seismic data (the vertical component and one of the horizontal components) in order to perform the joint velocity inversion.
In an even further embodiment, the method further comprises a down going and up coming layer stripping process to extract and balance the derived P-wave and S-wave interval velocities with depth-consistency. A velocity correction and balance is established to produce accurate interval velocities in each layer preventing the error propagation. It is a dynamic and iterative process to ensure the accuracy of the derived interval velocities for imaging earth sub-surface structure and extracting lithology information from acquired multicomponent seismic data.
In an even further embodiment, the method further comprises a time and depth conversion for both velocity field and seismic data. The time and depth conversion produces more accurate velocity field in depth allowing the construction of velocity model for pre-stack migration and other processing.
In a further embodiment, a new method and system of multicomponent geophysical exploration is disclosed utilizing joint velocity inversion to extract accurate P-wave and S-wave interval velocities from multicomponent seismic data.
In still a further embodiment, a method of seismic signal processing is provided. The method comprises receiving seismic data, and extracting at least one velocity from said seismic data.
In a further embodiment, a system of seismic signal processing is provided. The method comprises receiving seismic data, and extracting at least one velocity from said seismic data.
In an even further embodiment, a seismic data point is provided. The seismic data point is produced by a process comprising receiving seismic data; and extracting at least one velocity from said seismic data.